A conventional and well known technique for forming abrasive tools is to mix hard particles such as diamonds into a matrix material, and to exert pressure on the mixture while increasing the temperature of the mixture, to a temperature at which the matrix material is sintered. One technique for heating the mixture is to place the mixture between pressure plates, or plungers, formed of electrically conductive material, and to pass an electric current through the plungers and the mixture sufficient to raise the temperature to the necessary extent. In making tools according the these prior art techniques, the plungers are frequently formed of graphite. The graphite is a good conductor of the electrical current; but, if the hard particles protrude from the matrix material during sintering under pressure, the plunger will be damaged. The face of the plunger will have to be dressed, or the graphite portion will have to be replaced before further use If the plunger is formed of a hard metal rather than graphite, it will be understood that dressing the face will be more difficult, and more expensive.
In sintering material under pressure to make abrasive tools, it will be understood that the intent is to have the hard particles substantially embedded within the matrix material so the surface of the plunger will not be marred. Also, of course it is desired to provide a tool having the hard particles either uniformly distributed so the tool will wear evenly during use, or distributed according to a specific tool design to achieve particular cutting functions. If particles protrude from some areas of the surface, but not others, the aggressiveness of the tool will vary between the various areas of the tool, so a tool can be designed to accomplish any desired end.
In view of the above discussed techniques, it will be understood that, after a tool is sintered, the tool must be dressed to "open" the surface of the tool. That is to say, the matrix material must be removed on the working surface of the tool to expose the hard particles. This dressing of the tool is an additional step in the manufacturing process, and increases the total cost of manufacture.